In the papermaking field, for example, various papermaking chemicals such as retention aids and drainage aids so as to improve the runnability and work efficiency by improving the yield and water filtering property of pulp and/or fillers which are/is a raw material, and paper strengthening agents so as to improve the strength of paper products have been conventionally known.
As such a papermaking chemical, a paper strengthening agent made of an aqueous solution of a (meth)acrylamide polymer has been known, and to be specific, for example, it has been proposed that a (meth)acrylamide, a dimethylaminoethyl methacrylate, a quaternary compound of a dimethylaminoethyl methacrylate, an itaconic acid, a sodium methallylsulfonate, a methylene bisacrylamide (polyfunctional vinyl monomer), and deionized water are charged, and a polymerization initiator (ammonium persulfate) is added thereto to be reacted, so that the paper strengthening agent is obtained as an aqueous solution of an amphoteric polyacrylamide (ref: Patent Document 1).